Generally, in fish paste products such as kamaboko-type products which are typical and traditional Japanese fish paste products, both the starting materials and the final products have very homogeneous properties. Such properties are characterized by, for example, homogeneous cross sections and, in case of sliced products, tearing in almost linear rather than in zigzag fashion by application of a certain tensile force. In order to improve marketability, recently, there have been developed various paste products having heterogeneous properties, for example, kamabokos having patterns such as letters or figures appearing on their cross sections, chikuwas (which are one kind of kamaboko-type products having holes longitudinally extended through the centers thereof) with sticks of cheese or sausages inserted into these holes, and kamabokos with other solid edible ingredients such as cheese blocks scattered therein. However, these various marketed products having heterogeneous properties still have uniform patterns and artificial cross sections. Further, basically, these products still maintain the same homogeneous properties as those of the starting materials, i.e., semi-processed wet fish protein prepared from minced fish flesh, so-called, surimi.
In order to obtain a novel paste food product having heterogeneous properties which is completely different from the above products to further improve marketability of paste products, the present inventors have studied intensively. As the result, it has been found that the homogeneous properties of a paste product and its starting material such as surimi or minced meat can be modified by mixing an acidic paste with a protein-containing paste (hereinafter referred to as heat gellable protein paste) such as fish surimi in a low degree of homogeneity and heating the resulting mixture and that the product thus obtained is a livestock meat ham-like paste product having a heterogeneous cross section which tears in zigzag fashion when applying a tensile force. In addition, it has been found that the mixing of the acidic paste with the heat gellable protein paste and the molding of the product can be performed continuously, constantly, efficiently and sanitarily by using a static mixer which has not been hitherto used in the preparation of paste food products, particularly, mixing in a low degree of homogeneity.